CN109520532B - A multi-sensor multiplexing demodulation system and processing method of a fiber optic Faber sensor - Google Patents

Abstract

The invention relates to a multi-sensor multiplexing demodulation system and a processing method of an optical fiber Faber sensor, and belongs to the technical field of optical fiber sensing. The system is composed of broadband swept laser light source, optical circulator, wavelength division multiplexer, photoelectric detection module, spectrum restoration module and data processing module connected in sequence, and connected to N large-cavity-length optical fibers in parallel multiplexing mode. The processing method includes: S1: using a spectrum restoration module to restore the received interference spectrum into N-segment interference spectrum signals; S2: using the sparse sampling frequency demodulation method to process and calculate each segment of spectral data separately, Obtain the respective equivalent frequency values; S3: According to the relationship between the equivalent frequency value and the cavity length of the fiber Fa-Per sensor, respectively obtain the values of the N fiber Fa-Per sensors. The invention effectively solves the large-capacity parallel multiplexing problem of the white light interference type optical fiber Fa-Per sensor.

Description

A multi-sensor multiplexing demodulation system and processing method of a fiber optic Faber sensor

technical field

The invention belongs to the technical field of optical fiber sensing, and relates to a multi-sensor multiplexing demodulation system and a processing method of a white light interference type optical fiber Fa-Per sensor.

Background technique

White light interferometric fiber optic sensor is a fiber optic sensor that uses wide spectrum interference to achieve high-precision measurement. Compatibility, etc. Therefore, it has great application potential in special occasions such as petroleum, chemical industry, coal mine, machinery, and various flammable, explosive and harsh working environments.

Figure 2 shows the typical demodulation system principle of the optical fiber white light interferometry system, which consists of a low-coherence broadband light source (11), an optical coupler (12), a spectrometer (13), and a data processing unit (14). If the low-coherence broadband light source has the ideal broadband spectral characteristics of Fig. 3(a), it will reach the fiber Fa-Per sensor (21) through the transmission fiber and return to the broadband interference signal shown in Fig. 3(b). The data processing unit uses the corresponding demodulation algorithm to calculate and process the cavity length to complete the demodulation. Such a measurement system has the advantages of simple structure, mature technology and easy implementation. However, it is difficult to realize multi-sensor multiplexing, which restricts its large-scale engineering application.

For the multi-sensor multiplexing problem of white light interferometric sensors, there are mainly two multiplexing technologies: time division multiplexing and frequency division multiplexing. Time division multiplexing uses an optical switch to switch the light source to multiple sensors and demodulate them in time. Although it enables each sensor to have the same demodulation accuracy, the switching of the optical path limits the overall measurement speed of the system, and the mechanical The long-term reliability of the switching structure is low. Frequency division multiplexing obtains the interference spectral signals of several sensors with different cavity lengths L at the same time, and then performs spectrum analysis on the interference spectral signals, and uses different peaks on the spectrum to distinguish the sensors; because it requires the cavity length of each fiber Fa-Per sensor Different, the number of reuse is small, and the practicability is poor.

Therefore, the multi-sensor multiplexing of white light interferometric fiber optic sensors has become one of the bottlenecks restricting the large-scale application of such sensors.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a multi-sensor multiplexing demodulation method and system for a white light interference fiber optic sensor. The combined solution of the Perspective sensor, coupled with the wavelength division multiplexer matching the wavelength range of the light source, and the subsequent sparse spectrum sampling and demodulation algorithm, can effectively solve the white light interference type fiber Faber sensor without reducing the contrast of the coherent signal. The large-capacity parallel multiplexing problem.

To achieve the above object, the present invention provides the following technical solutions:

A multi-sensor multiplexing demodulation system of a white light interference type optical fiber Fa-Per sensor, the system is shown in FIG. , a photoelectric detection module (104), a spectrum restoration module (105) and a data processing module (106) are sequentially connected to form an N-channel multiplexing and demodulation system (1), and are respectively connected to N large-cavity-length fiber Fa-Per sensors (2). );

The frequency sweep laser has a narrow spectral line width and a wide frequency sweep range, so as to output a narrow line width sweep frequency laser beam with variable wavelength in a wider spectral range;

The optical circulator is used to unidirectionally transmit the swept-frequency laser beam emitted by the swept-frequency laser to the wavelength division multiplexer;

The wavelength division multiplexer is used to divide the laser signal in the swept spectral range into N channels of narrow-band spectral signals, which are respectively transmitted to N fiber Fa-Per sensors, and then the N channels of narrow-band spectral interference signals returned by the fiber Fa-Per sensor are returned. After merging, it is transmitted to the photoelectric detection module through the optical circulator;

The photoelectric detection module is used to convert the interference signals returned from the N fiber Faber sensors into electrical signals that vary with time, and then convert them into discrete digital electrical signals through amplification and sampling;

The spectral restoration module is used to convert the time domain scanning interference spectral signal into the interference spectral signal of the spectral wavelength domain;

The data processing module is used for demodulating the interference spectrum signal to calculate the cavity length value of the N fiber Fa-Per sensors.

Further, each of the N optical fiber Fa-Per sensors with large cavity length should satisfy L _min <L<L _max , so as to ensure that each sensor can generate enough interference fringes to satisfy Requirements for subsequent demodulation calculations.

The upper limit L _max and the lower limit L _min of the cavity length of the optical fiber Fa-Per sensor satisfy the following two equations respectively:

where FMHW is the spectral linewidth of the swept-frequency laser, Δλ and _λc are the swept spectral range and the center wavelength of the swept-frequency laser light source respectively (as shown in Figure 4); and the spectral bandwidth B of one channel of the wavelength division multiplexer (as shown in Figure 5(a)), the number of channels N and the frequency interval δf satisfy the following two formulas:

N=Δλ/B (3)

Further, a multi-sensor processing method applicable to the demodulation system includes the following steps:

S1: Use the spectrum restoration module to restore the received interference spectrum to the N-band interference spectrum signal;

S2: Use the frequency demodulation method of sparse sampling to process and calculate each segment of spectral data separately to obtain their respective equivalent frequency values;

S3: According to the relationship between the equivalent frequency value and the cavity length of the fiber Fa-Per sensor, the values of N fiber Fa-Per sensors are calculated respectively.

The beneficial effects of the present invention are as follows: the present invention combines a swept-frequency laser light source with a narrow spectral line width and a wide sweep frequency range with a large-cavity-length fiber Fa-Per sensor, and is equipped with a wavelength division multiplexer to perform N-way spectral division, thereby achieving The spectral bandwidth occupied by each sensor is reduced without reducing the contrast of coherent signals; and the frequency demodulation method of sparse sampling is used to demodulate and calculate the interference spectral signals of N fiber optic sensors to ensure the narrowband spectrum. The demodulation accuracy of the signal; thus effectively solve the large-capacity parallel multiplexing problem of the white light interference type fiber optic sensor.

Description of drawings

In order to make the purpose, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for description:

Fig. 1 is the structure diagram of the multiplexed white light interference fiber Fabry measurement system;

Fig. 2 is the schematic diagram of the demodulation system of the existing typical white light interferometric method Perspective sensor;

Figure 3 is a spectrum diagram of a white light interference fiber Fa-Per sensor, in which Figures 3(a) and 3(b) are the ideal spectrum of a low-coherence light source and the corresponding interference spectrum output of the fiber-based Fa-Per sensor. ;

Fig. 4 is the spectral schematic diagram of the swept-frequency laser light source; Fig. 4 (a) is the spectral scanning process of the output narrow linewidth of the swept-frequency laser; Fig. 4 (b) is its swept-frequency spectral range;

Figure 5 is a schematic diagram of the multiplexing of interference signals in this method; Figure 5 (a) is a spectral characteristic diagram of an N-way wavelength division multiplexer; Figure 5 (b) is a respective interference spectrum diagram of the N-way optical fiber Fa-Per sensor;

Fig. 6 is the principle flow chart of the demodulation algorithm of sensor multiplexing spectrum;

FIG. 7 is a structural diagram of the parallel multiplexed fiber Fa-Per measurement system according to the first embodiment;

FIG. 8 is a structural diagram of the parallel multiplexed optical fiber Faroese measurement system according to the second embodiment.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, a broadband frequency sweep laser 101, an optical circulator 102, a wavelength division multiplexer 103, a photoelectric detection module 104, a spectrum restoration module 105 and a data processing module 106 are sequentially connected to form an N-channel multiplexing and demodulation system 1, and connect N large cavity length fiber Fa-Per sensors 2;

The broadband swept laser 101 is used to provide a laser light source with variable wavelength in a wide spectral range; the optical circulator 102 is used to unidirectionally transmit the broadband swept laser signal emitted by the light source to the wavelength division multiplexer, At the same time, the optical signal returned by the wavelength division multiplexer is unidirectionally transmitted to the photoelectric detection module; the wavelength division multiplexer 103 is used to divide the broadband light into N channels of narrowband light with multiple wavelengths, and transmit them to N long-band lights respectively. The cavity length fiber Fa-Per sensor, and then the interference light signal returned by the fiber Fa-Per sensor is combined and returned to the optical circulator; the photoelectric detection module 104 is used to convert the wavelength-scanned interference laser signal into a time-varying electrical signal, and then return to the optical circulator. After amplification, sampling and conversion into discrete digital electrical signals; the spectral restoration module 105 is used to convert the time domain scanning interference spectral signal into the interference spectral signal of the spectral wavelength domain; the data processing module 106 is used to extract the interference spectral signal from the interference spectral signal. The cavity length values of N fiber sensors are calculated by one-time demodulation.

The broadband light source provided by the swept-frequency laser is shown in Figure 4. The output of the light source at any time is a narrow-spectrum laser with a spectral bandwidth of FWHM as shown in Figure 4(a). When it scans with time, its The final swept spectral range is shown in Figure 4(b).

The spectral characteristics of the wavelength division multiplexer are shown in Figure 5(a), a filter channel is equivalent to a spectral narrowband filter, which outputs a wavelength of light to the corresponding port, and is connected to a fiber optic Fa-Per sensor, thus The multiplexed interference spectrum is obtained as shown in Fig. 5(b).

The demodulation algorithm consists of three steps, as shown in Figure 6: First, the spectrum is divided into N segments, and then the frequency demodulation algorithm of the sparse spectrum is used to demodulate and calculate the interference spectrum signals of each segment respectively, so as to obtain the respective N fiber Fa-Per sensors. The equivalent angular frequency is finally converted into the cavity length of the fiber Fa-Per sensor, thereby completing the cavity length demodulation of N fiber Fa-Per sensors.

In order to ensure the signal-to-noise ratio of the interference signal, the N-fiber Fa-Per sensor adopts a Fa-Per sensor with a large cavity length.

For the N fiber-optic Fa-Per sensors with large cavity lengths, each cavity length L should satisfy L _min < L < L _max , to ensure that each sensor can generate enough interference fringes to satisfy the subsequent solution. Adjustment calculation requirements.

The upper limit L _max and the lower limit L _min of the cavity length of the fiber Fa-Per sensor should satisfy the following two equations respectively:

where FMHW is the spectral linewidth of the swept-frequency laser, Δλ and _λc are the swept spectral range and the center wavelength of the swept-frequency laser light source respectively (as shown in Figure 4); and the spectral bandwidth B of one channel of the wavelength division multiplexer (as shown in Figure 5(a)), the number of channels N and the frequency interval δf satisfy the following two formulas:

N=Δλ/B (3)

The wavelength division multiplexer, the photoelectric detection module, the spectrum restoration and demodulation module and the implementation platform of the demodulation algorithm involved in the method and system have various implementation schemes. The present invention proposes two sets of specific implementation cases:

1. Example 1

The system principle of this embodiment is shown in FIG. 7 . In this system, the light source adopts a communication C-band MEMS type swept frequency laser 111 ; the wavelength division multiplexer adopts an arrayed waveguide grating type wavelength division multiplexer (AWG-DWDM) 113 ; The detection module is composed of an indium gallium arsenide high-speed photodetector (InGaAs-PD) 114, a signal amplification circuit 115 and a high-speed ADC acquisition circuit 116; the spectrum reduction module 117 of the FPGA is used to divide and restore the signal into N-segment interference spectrum signals, and transmit them to The PC 118 realizes the demodulation calculation of the N cavity lengths by the Labview program.

2. Embodiment 2

The system principle of this embodiment is shown in Figure 8. In this system, the light source adopts the communication C+L band scanning grating feedback type sweep frequency laser 121; the wavelength division multiplexer adopts the volume phase holographic grating type dense wavelength division multiplexer (VPH). -DWDM) 123, the photoelectric detection module is composed of a germanium high-speed photodetector (Ge-APD) 124 with its own gain and a high-speed AD acquisition circuit 125. The spectrum restoration module adopts the ARM processing module 126 to realize the restoration of N-channel spectrum; the high-speed DSP data processing system 127 is used for processing and calculation, and the embedded software is used to complete the demodulation calculation of N cavity lengths.

3. Implementation effect

For the Fa-Per sensor multiplexing scheme shown in Figure 1, if a swept-frequency laser light source with a communication C-band bandwidth of 35nm and a wavelength division multiplexer with a channel frequency interval of 100 GHz in the international communication standard G.694.1 are used, the fiber Fa-Per sensor If the cavity length satisfies formula (1) and formula (2), a 40-channel fiber optic Fa-Per sensor multiplexing system can be realized, and it is ensured that all interference sensors do not interfere with each other and sense independently.

Since the information of all sensors can be obtained in one spectral acquisition, and the measurement speed of the system is determined by the spectral sweep speed of the swept-frequency laser, the increase in the number of multiplexed sensors in this scheme will not reduce the overall measurement speed of the system. Therefore, the system of the present invention uses a commercially available high-speed frequency sweep laser to achieve a multiplexing and demodulation rate of more than 1 kHz for dozens or hundreds of optical fiber sensors.

Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should Various changes may be made in details without departing from the scope of the invention as defined by the claims.

Claims (3)

1. A multi-sensor multiplexing and demodulating system of an optical fiber Fabry-Perot sensor is characterized in that the system is formed by sequentially connecting a frequency sweeping laser (101), an optical circulator (102), a wavelength division multiplexer (103), a photoelectric detection module (104), a spectrum reduction module (105) and a data processing module (106) to form an N-channel multiplexing and demodulating system (1) and respectively connecting N large-cavity long optical fiber Fabry-Perot sensors (2);

the sweep-frequency laser has narrow spectral linewidth and wide sweep-frequency range so as to output a narrow linewidth sweep-frequency laser beam with variable wavelength in a wide spectral range;

the optical circulator is used for transmitting the swept frequency laser beam emitted by the swept frequency laser to the wavelength division multiplexer in a single direction;

the wavelength division multiplexer is used for dividing laser signals in a sweep frequency spectrum range into N paths of narrow-band spectrum signals, respectively transmitting the signals to N optical fiber Fabry-Perot sensors, combining N paths of narrow-band spectrum interference signals returned by the optical fiber Fabry-Perot sensors, and transmitting the signals to the photoelectric detection module through the optical circulator;

the photoelectric detection module is used for converting an interference laser signal scanned by wavelength into an electric signal which changes along with time, and then converting the electric signal into a discrete digital electric signal through amplification and sampling;

the spectrum restoration module is used for converting the time domain scanning interference spectrum signal into an interference spectrum signal of a spectrum wavelength domain;

and the data processing module is used for demodulating and calculating the cavity length values of the N optical fiber Fabry-Perot sensors according to the interference spectrum signals.

2. The multi-sensor demultiplexing system according to claim 1, wherein said large cavity length fiber Fabry-Perot sensor has a cavity length L satisfying L_min<L<L_maxTo ensure sufficient signal contrast of the interference spectral signal, where L_maxAnd L_minRespectively satisfy the following formula:

wherein FMHW is the full width half wave, lambda of the sweep laser line_cThe central wavelength of the sweep frequency laser light source; the spectral bandwidth of one channel of the wavelength division multiplexer is B, and the wavelength division multiplexing number N which can be accommodated in the sweep frequency spectral range delta lambda of the sweep frequency laser light source meets the following formula:

N＝Δλ/B (3)。

3. multi-sensor processing method applicable to a demodulation system according to claim 1, characterized in that it comprises the following steps:

s1: restoring the received interference spectrum into an N-section interference spectrum signal by using a spectrum restoring module;

s2: respectively processing and calculating each section of spectral data by using a frequency demodulation method of sparse sampling to obtain respective equivalent frequency values;

s3: and respectively solving the values of the N optical fiber Fabry-Perot sensors according to the relation between the equivalent frequency value and the cavity length of the optical fiber Fabry-Perot sensors.

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